Network Working Group K. Hamzeh
Request for Comments: 2107 Ascend Communications
Category: Informational February 1997
Ascend Tunnel Management Protocol - ATMP
Status of this Memo
This memo provides information for the Internet community. This memo
does not specify an Internet standard of any kind. Distribution of
this memo is unlimited.
IESG Note:
This note documents a private protocol for tunnel management. This
protocol is NOT the product of an IETF working group nor is it a
standards track document. There is ongoing effort in an IETF working
group which could result in a standards track document which
specifies a protocol which provides similar functionality.
Abstract
This document specifies a generic tunnel management protocol that
allows remote dial-in users to access their home network as if they
were directly attached to the home network. The user's client
software uses an address contained in the home network address space
for the remote access. Packets to and from the home network are
tunneled by the Network Access Server (NAS) to which the user
connects and a Home Agent (HA) on the user's home network. This
allows for the support of access to Virtual Private Networks and also
allows for the use of protocols other than IP to be carried over the
tunnel. An example of how the RADIUS (Remote Authentication Dial In
User Service) can be used to provide the necessary configuration
information to support this service is also provided.
1. Introduction
The Ascend Tunnel Management Protocol (ATMP) is a protocol currently
being used in Ascend Communication products to allow dial-in client
software to obtain virtual presence on a user's home network from
remote locations. A user calls into a remote NAS but, instead of
using an address belonging to a network directly supported by the
NAS, the client software uses an address belonging to the user's
"Home Network". This address can be either provided by the client
software or assigned from a pool of addresses from the Home Network
address space. In either case, this address belongs to the Home
Network and therefore special routing considerations are required in
Hamzeh Informational [Page 1]RFC 2107 ATMP February 1997
order to route packets to and from these clients. A tunnel between
the NAS and a special "Home Agent" (HA) located on the Home Network
is used to carry data to and from the client.
ATMP currently allows for both IP and IPX protocols to be tunneled
between the NAS and the HA. The protocol to be used, the HA to use,
and other user specific information is provided by some configuration
mechanism that is beyond the scope of this document. Appendix A
illustrates how RADIUS [5] is used to convey this information to the
NAS.
The determination of the Home Network address to be used can be
accomplished in different ways. It could, for example, be configured
in the client and negotiated by IPCP (or IPXCP). Alternatively, it
could be defined to be an address specific to the given user ID, or
it could be assigned from a pool of addresses provided by the Home
Network for the purpose of remote dial-in access. Again, how this
address is assigned and how the NAS decides to invoke ATMP for a
specific call is beyond the scope of this document.
1.1 Protocol Goals and Assumptions
The ATMP protocol is implemented only by the NAS and HA. No other
systems need to be aware of ATMP. All other systems communicate in
the normal manner and are unaware that they may be communicating with
remote clients. The clients themselves are unaware of ATMP. It is
assumed that standard PPP [8] (or SLIP) clients are being used.
Unlike the mobile-IP protocol [3], ATMP assumes that a single NAS
will provide the physical connection to a remote client for the
duration of the session. The client will not switch between NASes
expecting to keep the same IP address and all associated sessions
active during these transitions. A particular client can be
registered with a given HA only once at any given time.
Deregistration with a HA implies loss of all higher layer sessions
for that client.
IP multicasting is currently not provided by ATMP.
1.2 Terminology
The terminology used in this document is similar to that used in
mobile-IP. As pointed out in the previous section, however, ATMP
provides a subset of the functionality provided by mobile-IP and the
meanings of the various terms used herein have been modified
accordingly.
Hamzeh Informational [Page 2]RFC 2107 ATMP February 1997